It’s that time again. The fifth report by the Intergovernmental Panel on Climate Change (IPCC) is being rolled out today with the release of a Summary for Policymakers for the climate science portion of the report. (Sections on impacts of climate change and mitigation strategies will be released in the coming months.) Suspense about what the report would include has been somewhat deflated by leaks of early drafts, but the final wording is now available.

The group that prepared the report on the physical science behind climate change consisted of 259 climate scientists from 39 countries. (During a press conference, IPCC Chairman Rajendra Pachauri noted that in total, 831 scientists contributed to the various sections of the report, nearly 60 percent of whom were not involved with past reports.) The purpose of the report is to summarize what scientists have learned about climate change and to convey the level of scientific confidence in each conclusion. It cites 9,200 peer-reviewed papers, two-thirds of which were published after the release of the last IPCC report in 2007.

After being drafted by a number of scientists, the Summary for Policymakers was reviewed line-by-line by representatives of nations from around the world this week. Proposals for clarifying language then had to be approved by the scientists before the final draft was released.

Word on the street

Attention was drawn to a few elements of the leaked drafts of the reports, and we can now see how they appear in the finalized summary. First, the report does indeed express a higher confidence in the human causation of climate change than previous reports. Specifically, it states, “It is extremely likely [a phrase used to represent greater than 95 percent confidence] that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.”

Second, the range of best estimates for climate sensitivity (a measure of how much warming results from a given increase in greenhouse gases) did expand a bit, now spanning 1.5 to 4.5 degrees Celsius for a doubling of CO2. The 2007 IPCC report gave a range of 2.0 to 4.5 degrees Celsius.

Also, estimates of sea level rise have increased from those in the last report, which were conservative due to uncertainty about the behavior of Greenland and Antarctica. The middle of the road scenarios for future emissions now project 0.32 to 0.62 meters of sea level rise by the last couple decades of the 21st century. The high emissions scenario would result in an estimated 0.52 to 0.98 meters by the year 2100.

The gist

As expected, the slowdown in atmospheric warming over the past few years was considered, although the cutoff date for including studies unfortunately excluded some recent, relevant ones. The report explains that the 2000s have seen some cooling influence from a slight lull in radiation from the Sun, a number of volcanic eruptions, and natural variability in the ocean (namely, a rash of cool La Niñas). It also offers a reminder that climate models “are not expected to reproduce the timing of internal variability." That is, no climate scientists hazard predictions about when El Niños, La Niñas, and volcanic eruptions will be on tap.

This iteration of the IPCC report used a new, simplified set of scenarios for future emissions. So although the graphs look a little different from past ones, the projections haven’t really changed. The middle-of-the-road scenarios would result in about 1 to 3 degrees Celsius of warming by the end of the century, and the high-emissions scenario yields 2.6 to 4.8 degrees Celsius.

In order to keep warming below the oft-referenced target of 2 degrees Celsius above pre-industrial temperatures, the total amount of carbon humans have emitted cannot exceed about 800 gigatons, the report says. As of 2011, about 531 gigatons had been emitted. The two middle scenarios involve the emission of 595-1250 gigatons between now and the end of the century.

The report also emphasizes the need to consider the long-term ramifications of carbon dioxide emissions. “Depending on the scenario, about 15 to 40 percent of emitted CO2 will remain in the atmosphere longer than 1,000 years.”

Same as it ever was

To be clear, we’re sweating the details here. There’s nothing Earth-shattering in this report. The first IPCC report in 1990 laid out the big picture: our greenhouse gas emissions are changing the climate, and avoiding dangerous amounts of warming requires a rapid transition away from generating those emissions. The science has progressed a great deal since then, but the basic conclusions have not changed.

The IPCC reports are meant to provide governments (and everyone else) the best available information on which to base decisions about how to deal with the problem. Obviously, the reports haven’t guaranteed that those decisions get made.

The full text of the report will be released on Monday, after which we’ll be able to take a closer look at the (sweaty) details. On Saturday morning, from 7:00-9:00am EDT, a presentation and discussion of the report will be streamed live from Stockholm if you’d like to hear from some of the scientists who led the effort.

443 Reader Comments

No decisions will be made, unfortunately. At least, not here in the United States. Our dysfunctional political system will not deal with this report at the national level with all the misinformation and pseudoscience out there.

No decisions will be made, unfortunately. At least, not here in the United States. Our dysfunctional political system will not deal with this report at the national level with all the misinformation and pseudoscience out there.

No decisions will be made, unfortunately. At least, not here in the United States. Our dysfunctional political system will not deal with this report at the national level with all the misinformation and pseudoscience out there.

The best we can hope for is smart decisions at the local level.

And while I'd like to believe that when we start playing out scenes from sci-fi/disaster movies, the politicos will rise to the occasion, I think it more likely they'll go Monty Python and "RUN AWAY, RUN AWAY!"

We need to start preparing for the worst, while hoping for the best. This means infrastructure changes and plans to move low coastal populations inland. I don't hold much hope for any global solution to change the climate itself. We can slow things down, make minor changes perhaps, but we will have to plan to adapt to these changes.

Climate denialists are only interested in one thing; continuing to believe that they know the "truth", that it's all a giant conspiracy by the world governments to mobilise people, or tax people, or do something horrible. They want to feel special, that they, and their friends know the truth while the sheep continue to buy the official story.

"The report explains that the 2000s have seen some cooling influence from a slight lull in radiation from the Sun, a number of volcanic eruptions, and natural variability in the ocean (namely, a rash of cool La Niñas)"

I don't see how these three things can be considered together. The sun and volcanoes are external influences on the climate; it's obvious to anyone how they would affect the climate.

But ocean currents, ninas or ninos or whichever one, are part of, and driven by, the climate. It seems to me like it's saying the climate cooled a bit, because it got cooler.

How is it that an ocean current can be considered an external forcing on climate?

Even if this is true, it begs the question of just how much we ought to sacrifice to prevent it. Do we all take major hits to our standard of living just so the climate, which changes all the time anyway, stays the same just a little longer.

And the people likely to suffer most are the ones without the resources to adapt. Namely the developing world. Not your problem, right? Social instability in other countries has never affected us before, so why worry? /s

They’re still misleading the public. Everyone knows (well, many of us know) their models can’t simulate the natural processes that cause surface temperatures to warm over multidecadal timeframes, yet they insist on continuing this myth.

It appears the climate science community, under the direction of the IPCC, is still not interested in being honest within itself or with the public. What a shame!

On this sort of thing, I like to apply Occam's razor. Which is more likely: A massive global conspiracy of practically all the climate scientists out there to deceive the public, or that they're mostly honest scientists trying to find facts and understand the world? On top of that, there's the fact that when a single scientist points out a major flaw in existing models that single scientist usually wins a Nobel.

Ok, so then, we all agree its a problem and we need to act now to fix it right?

Then someone please lay out how we fix this? Replace all our coal power plants...great idea, they're dirty, and not only are they dirty, we have to ship tons of coal all over the place to fuel them. So what do we replace them with? Nuclear? Its the cleanest, and statistically safest, despite what anti-nuclear activists believe. But too many people are scared off because "omg, teh nukluar plants will leak radiation!!!". So that won't happen. Wind? Not feasible for everywhere. Solar? Again, not feasible for everywhere, and the eco-nuts are blocking them all over the place because they take up a bunch of land. Hydroelectric? Again, eco nuts don't like that, because it destroys ecosystems and prevents fish migrations (i actually agree with this, we don't need any more hydro plants).So...What do we replace our dirty coal with? And where do we get the billions of dollars to do it?

Next, ok, we all agree our cars are filthy, we need to do something to replace all the internal combustion engines out there. So...how exactly do we replace everybody's car on the entire planet? We don't even have a viable replacement yet. And where does the money come from? And what do we do with the existing cars...force everyone to stop driving them (that will go over real well)?

Yes we should do something, but I have yet to ever see anyone propose any practical solutions that could actually work, that people will actually agree with. Have I missed anything out there?

How many times do the massive majority of climate scientists have to explain that we're dooming ourselves before people stop claiming it's still up for debate? Of course evolution is still "just a theory" to them, so I don't know why I expect this to ever change.

Even if this is true, it begs the question of just how much we ought to sacrifice to prevent it. Do we all take major hits to our standard of living just so the climate, which changes all the time anyway, stays the same just a little longer.

You're arguing from a grave assumption that is not true.

"Do we all take major hits to our standard of living"... Who said we need to? The costs of mitigation have been considered by others in the past (Garnaut, Stern) and they've found that on the contrary, mitigation is actually cheaper and more cost-effective (i.e. of lesser impact to our standards of living) than doing nothing.

Wind power by some accounts is getting comparable to coal in costs, solar energy has plumetted in price. Who's to say we can't eventually make renewables far cheaper than fossil fuels?

We went from zero to putting a man on the moon in 10 years, we invented the atomic bomb in 5 years... Human's capacity to innovate and find solutions is amazing... This is a great opportunity to invest in new technologies and to remove dependencies on a limited and geopolitically complicated supply of fossil fuels (that's just a bonus in addition to saving us from the worst of climate change).

Vast majority of the money supports the opposite of this conclusion. If what they're saying is wrong, why haven't those companies (eg coal and gas giants) sponsored solid reports refuting all the claims? The scientists would get a big kudos if it were a robust study, and the global warming claims would be completely undermined. Instead they seem to focus on using the media to spread the idea that there's some massive, international conspiracy between scientists to make people believe this were true.

They’re still misleading the public. Everyone knows (well, many of us know) their models can’t simulate the natural processes that cause surface temperatures to warm over multidecadal timeframes, yet they insist on continuing this myth.

Firstly, what natural processes did you fail to cite there?

Secondly, pretty sure the climate models that show global warming over fifty years due to carbon dioxide levels are working just fine on multidecadal time frames.

Ok, so then, we all agree its a problem and we need to act now to fix it right?

Then someone please lay out how we fix this? Replace all our coal power plants...great idea, they're dirty, and not only are they dirty, we have to ship tons of coal all over the place to fuel them. So what do we replace them with? Nuclear? Its the cleanest, and statistically safest, despite what anti-nuclear activists believe. But too many people are scared off because "omg, teh nukluar plants will leak radiation!!!". So that won't happen. Wind? Not feasible for everywhere. Solar? Again, not feasible for everywhere, and the eco-nuts are blocking them all over the place because they take up a bunch of land. Hydroelectric? Again, eco nuts don't like that, because it destroys ecosystems and prevents fish migrations (i actually agree with this, we don't need any more hydro plants).So...What do we replace our dirty coal with? And where do we get the billions of dollars to do it?

Next, ok, we all agree our cars are filthy, we need to do something to replace all the internal combustion engines out there. So...how exactly do we replace everybody's car on the entire planet? We don't even have a viable replacement yet. And where does the money come from? And what do we do with the existing cars...force everyone to stop driving them (that will go over real well)?

Yes we should do something, but I have yet to ever see anyone propose any practical solutions that could actually work, that people will actually agree with. Have I missed anything out there?

Sadly you're right, nuclear probably is the best clean option at present, but nobody is interested in increasing their nuclear power because of their concerns about radiation. One option for this would be to push money into liquid fueled versions such as the liquid thorium reactors, which are supposedly both safer and more efficent, with less radioactive waste at the end too. These are a bit of a long shot though, despite being implemented in some countries there's still serious issues which we don't know if we can fix

Climate denialists are only interested in one thing; continuing to believe that they know the "truth", that it's all a giant conspiracy by the world governments to mobilise people, or tax people, or do something horrible. They want to feel special, that they, and their friends know the truth while the sheep continue to buy the official story.

I wouldn't say that I am personally a denialist, I would say it is likely overblown to incite fear and movement on the topics that need movement.

However my concern is that repeatedly throughout history when something needs to change for the collective benefit we do it. For example; California and Smog. When the issue came up they capped the amount of emissions. They took a concrete step that prevented further damage.

When CFC's began tearing a hole in the ozone layer we had an immediate worldwide ban on them. Now the Ozone layer is rebounding.

We didn't come up with cap and trade in either case. Why? because it doesn't solve any problem.

If the recommended action for climate change was 'cap and violators will be shot', or 'cap and non-compliant factories will be bulldozed at your expense' I would be on board. Cap and Trade is a tax that will not improve the situation. at all.

Climate denialists are only interested in one thing; continuing to believe that they know the "truth", that it's all a giant conspiracy by the world governments to mobilise people, or tax people, or do something horrible. They want to feel special, that they, and their friends know the truth while the sheep continue to buy the official story.

That's a pretty broad brush you are using there. There are plenty of people like myself. I do believe we have affected the environment in fairly obvious ways. I don't believe that we will catastrophically affect the planet in the next 100 years. I think we should continue to challenge the models which are used to predict such catastrophic outcomes, because they are too simplistic and don't take into account too many variables. I think it is significant that the warming trend was below the lowest parameters of the prediction range because it showcases these flaws in the models.

Regardless of that, I don't think from a political standpoint that using these reports and predictions as leverage to enact change is ever going to work. Aside from the fact that they essentially glossed over the huge errors in their predictions over the last 15 years, I think that most people on both sides just don't care about reducing their carbon footprint (the obvious hypocritical examples from Hollywood are just the surface).

So we should focus efforts in other ways and with other arguments. Carbon is an illusive concept, but pollution is not for most. Better gas mileage or reliable alternative energy sources are simply better carrots than global warming. Companies like Tesla can help radically change behavior by truly innovating. It's why I own the stock and will someday own a Tesla. Promote more nuclear power, promote cleaner coal and natural gas. Show people how they can BENEFIT in tangible ways outside of simply helping combat global warming and they will react.

Even if I am completely wrong regarding the next 100 years the topic has become too polarizing to ever gain real traction. So for those of you truly concerned about it, find another way to enact change.

Even if this is true, it begs the question of just how much we ought to sacrifice to prevent it. Do we all take major hits to our standard of living just so the climate, which changes all the time anyway, stays the same just a little longer.

You're arguing from a grave assumption that is not true.

"Do we all take major hits to our standard of living"... Who said we need to? The costs of mitigation have been considered by others in the past (Garnaut, Stern) and they've found that on the contrary, mitigation is actually cheaper and more cost-effective (i.e. of lesser impact to our standards of living) than doing nothing.

Wind power by some accounts is getting comparable to coal in costs, solar energy has plumetted in price. Who's to say we can't eventually make renewables far cheaper than fossil fuels?

We went from zero to putting a man on the moon in 10 years, we invented the atomic bomb in 5 years... Human's capacity to innovate and find solutions is amazing... This is a great opportunity to invest in new technologies and to remove dependencies on a limited and geopolitically complicated supply of fossil fuels (that's just a bonus in addition to saving us from the worst of climate change).

Then we shouldn't have to subsidize or mandate it right. It should happen through normal market forces, which I am perfectly OK with.

Except that the reason that wind and solar are finally becoming viable are because of government funded research and subsidies to get the companies off the ground. The established energy companies had absolutely no reason to ever research technology that would make their entire business model obsolete, and barriers to entry make it pretty much impossible that a free market solution would ever have made either technology happen. Certainly not before catastrophic damage had been done.

They’re still misleading the public. Everyone knows (well, many of us know) their models can’t simulate the natural processes that cause surface temperatures to warm over multidecadal timeframes, yet they insist on continuing this myth.

It appears the climate science community, under the direction of the IPCC, is still not interested in being honest within itself or with the public. What a shame!

The IPCC is actually prepared to dismiss the pause in warming as irrelevant ‘noise’ associated with natural variability. Under pressure, the IPCC now acknowledges the pause and admits that climate models failed to predict it. The IPCC has failed to convincingly explain the pause in terms of external radiative forcing from greenhouse gases, aerosols, solar or volcanic forcing; this leaves natural internal variability as the predominant candidate to explain the pause. If the IPCC attributes to the pause to natural internal variability, then this begs the question as to what extent the warming between 1975 and 2000 can also be explained by natural internal variability. Not to mention raising questions about the confidence that we should place in the IPCC’s projections of future climate change.

If everything you propose is true -- what's the end game? Why would the IPCC, and all climatologists the world over hope to gain from fooling us sheeple?

They’re still misleading the public. Everyone knows (well, many of us know) their models can’t simulate the natural processes that cause surface temperatures to warm over multidecadal timeframes, yet they insist on continuing this myth.

It appears the climate science community, under the direction of the IPCC, is still not interested in being honest within itself or with the public. What a shame!

The IPCC is actually prepared to dismiss the pause in warming as irrelevant ‘noise’ associated with natural variability. Under pressure, the IPCC now acknowledges the pause and admits that climate models failed to predict it. The IPCC has failed to convincingly explain the pause in terms of external radiative forcing from greenhouse gases, aerosols, solar or volcanic forcing; this leaves natural internal variability as the predominant candidate to explain the pause. If the IPCC attributes to the pause to natural internal variability, then this begs the question as to what extent the warming between 1975 and 2000 can also be explained by natural internal variability. Not to mention raising questions about the confidence that we should place in the IPCC’s projections of future climate change.

If everything you propose is true -- what's the end game? Why would the IPCC, and all climatologists the world over hope to gain from fooling us sheeple?

Isn't it obvious? It's all part of a plan to overthrow the Illuminati to give the world over to the lizard people.

Climate denialists are only interested in one thing; continuing to believe that they know the "truth", that it's all a giant conspiracy by the world governments to mobilise people, or tax people, or do something horrible. They want to feel special, that they, and their friends know the truth while the sheep continue to buy the official story.

I wouldn't say that I am personally a denialist, I would say it is likely overblown to incite fear and movement on the topics that need movement.

However my concern is that repeatedly throughout history when something needs to change for the collective benefit we do it. For example; California and Smog. When the issue came up they capped the amount of emissions. They took a concrete step that prevented further damage.

When CFC's began tearing a hole in the ozone layer we had an immediate worldwide ban on them. Now the Ozone layer is rebounding.

We didn't come up with cap and trade in either case. Why? because it doesn't solve any problem.

If the recommended action for climate change was 'cap and violators will be shot', or 'cap and non-compliant factories will be bulldozed at your expense' I would be on board. Cap and Trade is a tax that will not improve the situation. at all.

How many of those things had giant well-moneyed interested fighting back and a sizeable contingent of our government believing that they were the ones who were right? Cap and Trade is an attempt to assuage concerns of artificial constraints by constraining the entire system while allowing the individuals in the system to trade (read: buy and sell) credits to where they are needed. The initial purchase could be seen as a tax, but then it acts like a stock, whose total supply decreases over time.

Then we shouldn't have to subsidize or mandate it right. It should happen through normal market forces, which I am perfectly OK with.

Oh typical "Free market magic will fix everything that needs fixing". Are you really that stupid? Its a wonder people that stupid can use a computer. If there existed this magical free market, then maybe it would prioritize renewable energy because it has better future prospects. But in reality, the economy is somewhere between a game played by human chickens running around with their heads cut off and freaking out at the slightest downturn in any quarterly profit, which pretty much prevents long term investments. To an oligarchy controlled by a very small number of people who's primary interest is in keeping themselves at the top, and maintaining the status quo. For them, its easier to keep using oil because it costs less than innovating new solutions, and oil will keep working for them for as long as they're alive so why bother. As for this mythical ability to break into the free market, between regulations, enormous investments required to start up a car company (just ask Elon) its not so free. Not to mention, that you have to sell to the dumbest animal on the planet, who won't buy electric cars because of no logical reason whatsoever. Studies have actually shown, those who don't believe in climate change will choose to pay MORE for a less environmentally friendly product. Trust me, the free market won't fix anything. You want more proof, Tesla a highly successful electric car company could only get an investment from the DoE, no private "free market" enterprise was willing to put dollars there. Well, that's a sufficiently long rant I think.

"The report explains that the 2000s have seen some cooling influence from a slight lull in radiation from the Sun, a number of volcanic eruptions, and natural variability in the ocean (namely, a rash of cool La Niñas)"

I don't see how these three things can be considered together. The sun and volcanoes are external influences on the climate; it's obvious to anyone how they would affect the climate.

But ocean currents, ninas or ninos or whichever one, are part of, and driven by, the climate. It seems to me like it's saying the climate cooled a bit, because it got cooler.

How is it that an ocean current can be considered an external forcing on climate?

The dynamics of heat transfer to and from the oceans to the atmosphere are very complex and difficult to model. The amount of extra heat being trapped by increased CO2 is easy to model.

We know there are climatic cycles on the order of decades that result in increased or decreased atmospheric temperatures (La Nina/El Nino being the most well-known). Over the long-term, they almost by definition have to average out to zero. (the overall heat in the system is the dominant effect).

The IPCC report refers to increased heat content in the oceans. The energy is still building up, that it's not being released into the atmosphere is just a result of natural variability.

What we do know is that there has been a dominant La Nina in the last 10 years. This normally produces cooler temperatures. Upon the trend line of increasing temperatures over the long-term, this La Nina 'cycle' has only resulted in a slower warming trend for the last 10 years.

In some ways the fact that it's still been getting warmer despite the conflation of a weaker solar output and the cyclical cooling of the atmosphere from a La Nina should be ringing alarm bells. Unfortunately, it seems for many it's not.